2 Answers
2

The performance index of the disk is based on its mechanical (eg: rotation speed) and electronic design (eg: cache size) and although you may be able to make some minor adjustments to its operating parameters using manufacturer-supplied tools (if available), you're stuck with what you have and the only way to improve your disk performance index would be to obtain a higher-spec disk.

Edit: Just discovered that the highest possible rating for a mechanical disk under Windows 7 is 5.9 anyway - 6 and above are reserved for SSDs: